1. Field of the Invention
This invention relates to storage and retrieval of data from a memory wherein blocks of data which are greater in length than one page can be stored in discontiguous portions of the memory.
2. Description of the Prior Art
In computer systems of the prior art in the event information is to be stored in peripheral memory, the host computer is provided with an indication of the amount of memory required to store the incoming information and proceeds to locate that space in memory by means of system software. Typically, when a controller transfers data between the host computer and any peripheral device, the host provided addresses in peripheral memory which the controller accesses are in sequential order and the system software typically maps the controller's transfers independently of the controller. Often a single block of storage area of sufficient size is not available in the memory in which case the host computer, by means of the system software, will note two or more discontiguous areas in memory for storage of the information therein. In this case, the system software finds a list of pages in memory in discontiguous areas that are available to be written into and sets up a transfer of information to the first page in the list via the controller. When the boundary or end of the first page is reached, the controller so advises the host and the host then provides the controller with the address of the second page, if it be discontiguous with said first page. This procedure continues until all of the information is stored in memory. It is readily apparent from the above that, after each page is stored in memory, storage temporarily ceases if the next page is discontiguous while the host is informed by the controller that the end of a page has been reached and the host then provides the controller with the address of the next page to be stored in memory and the number of transfers on that page. This procedure on a page by page basis is time consuming. The desire is to record information in discontiguous storage locations of memory in minimum time and with minimum disturbance of the host computer.